Electron beam tube



July 15, 1958 R. w. PETER 2,843,788

ELECTRON 'BEAM TUBE Filed Dec. 3. 1952 3 Sheets-Sheet 1 III I 11 11111 111 111 11 111 11! M H E07 INVENTOR.

POLFVW P575? Zea--- vIa 24% July 15, 1958 R. w. PETER I 2,843,788

ELECTRON BEAM TUBE Filed Dec. 3. 1952 3 Sheets-Sheet 2 mm ll l l'l l l l l'l l l 4 I :g 9 INIENTOR.

IITTORNEY July 15, 1958 R. w. PETER ELECTRON BEAM TUBE 3 Sheets-Sheet 3 Filed Dec. 3. 1952 R. m N m m United States Patent ELECTRON BEAM TUBE Rolf W. Peter, Princeton, N. J., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Application December 3, 1952, Serial No. 323,881

16 Claims. (Cl. 315-35) -by the source or cathode.

It has been proposed by Tien and Field in their article entitled Space charge waves in an accelerated electron stream for amplification of microwave signals, in the Proceedings of the Institute of Radio Engineers, vol. 40, No. 6, June 1952, page 688 et seq., to increase the amplitude of the fluctuating velocities and thereby amplify the alternating current voltage in an electron stream by subjecting the electron stream at suitable points therealong to changes in direct current voltage. While, as proposed, theoretically large changes in alternating current voltage amplitude are obtainable, in practice the results have heretofore fallen far short thereof. Furthermore, the efficiency of such devices has decreased with increasing electron stream current.

I have determined that inefiicient operation of such devices results from a potential drop across the electron stream, that is, in a direction normal to the axis or direction of flow of the stream. This potential drop across the stream represents differences in axial velocity of the electrons across the stream as distinguished from along the stream, and is difficult to control when the axial velocity of the stream is increased or decreased. I believe the theoretically attainable efiiciency is, among other things, dependent upon constant axial velocity of the electrons across the stream, and that the potential drop across the stream causes a loss in efficiency or merit. Furthermore, this potential drop and the corresponding loss in efficiency increases with increasing electron stream current and de creasing drift tube potential. This results in a limitation of the maximum current which may be utilized at a given electrode potential.

It is therefore a principal object of my invention to provide an electron device wherein a velocity modulated electron stream is subjected to velocity changes to change the amplitude of velocity fluctuations and in which the maximum change in amplitude is substantially greater than heretofore attained. A further object is the provision of such a device capable of effecting a greater increase in the amplitude of the velocity fluctuations along a velocity modulated electron stream than heretofore attainable.

Yet another object is the provision of an electron device in which the amplitude of noise fluctuations of electrons in a stream velocity modulated by an electron source is reduced to a minimum.

Still another object is the provision of a single beam space charge wave amplifier, in which a velocity modulated electron stream is subjected to direct current voltage changes, capable of enhanced gain and efliciency in operation.

A further object is the provision of a low noise, high power electron device such as a traveling-wave tube wherein the noise is eliminated to an extent which was heretofore unattainable.

In carrying out my invention I minimize and reduce to substantially zero the space charge depression of the axial velocity of electrons across an electron stream, which is subjected to direct current voltage changes, by providing a confining magnetic field such that the radially outward velocity component of the electrons in the electron stream caused by space charge is so counteracted or redirected that the electrons in a given cross section of the stream have the same axial velocity. Thus, in a preferred embodiment of my invention, wherein the electron stream is subjected to abrupt changes in direct current voltage, the axial confining magnetic field is also changed abruptly but in the opposite sense.

The novel features that are considered characteristic of my invention are set forth with particularity in the appended claims. The invention as well as additional objects and advantages thereof will be best understood from the following description when read in connection with the accompanying drawings, in which Figure l is a fragmentary perspective view partially in section of an electron device constructed in accordance with my invention;

Figure 2 is a diagram showing by the respective curves the relative distribution of alternating current i and velocity v along the beam path in Figure 1 and is oriented with respect to Figures 1 and 4;

Figure 3 is a diagram showing the constant axial electron velocity component across a given section of the stream in my invention, with the distribution of the same component without space charge compensation shown in broken line;

Figure 4 is a fragmentary view partially in section of another electron device constructed in accordance with my invention;

Figure 5 is a fragmentary sectional view of another electron device constructed in accordance with my invention and wherein electrodes which serve to vary the voltage also vary the magnetic field;

Figure 6 is a sectional view of a space charge wave amplifier device constructed in accordance with my invention;

Figure 7 is a sectional view of a low noise traveling wave tube constructed in accordance with my invention;

Figure 8 is a diagram showing the relative distribution of direct current voltage, magnetic field and alternating current velocity axially along the device of Figure 7; and

Figure 9 is a sectional view of another space charge wave amplifier constructed in accordance with my invention.

Referring now to the drawings in detail, one form of alternating voltage amplitude changer 10 in accordance with my invention is shown in detail in Figure 1. An array of electrodes 12, 13, 14 and 15 is mounted in a vacuum tight envelope 16 in spaced apart relation. Electrodes 12, 13, 14 and 15 are each connected to lead-ins which in utrn are adapted to be connected to a source of direct current potential in the "usual way. Electrodes 12, 13, 14 and 15 are alined axially and are so shaped and spaced, as is well known, that they function as accelerating and decelerating electrodes in accordance with the impressed direct current voltage. In the present instance, electrodes 12 and 14 :set up retarding direct current fields when energized and function as decelerating electrodes. Electrodes 13 and 15 establishxaccelerating direct our- Patented July 15, 1958 rent fields when energized and function as accelerating electrodes. Solenoids 17, 80, 81 and 82, which surround envelope 16, each function when energized to set up an axial magnetic field that is substantially homo- Y geneous within each solenoid but of difiierent field strength from the magnetic fields within the adjacent solenoids. Apertured disc shaped shields 18, 19, 20 of magnetic .material are each mounted so as to extend into the gap between adjacent electrodes while shields 21, 22 are mounted one at each end of the electrode array. It is to be understood that the shields do not extend far enough toward the axis of the beam to be impinged upon by the electrons.

In operation, an electron source, including a cathode,

. not shown in Figure 1, projects a stream of velocity modulated electrons along the axis of the array of shields and electrodes, as for example, in the direction left to right as viewed in the drawing. At the gap represented at the left end (Figure 1) of electrode 12, the electrons are decelerated inasmuch as electrode 12 is maintained at a low direct current voltage which is negative to the next following electrode and to the next preceding electrode, such as for example may be included in an elec tron gun structure. After crossing the aforementioned gap the electrons, having a low velocity corresponding to the potential of electrode 12, drift in the drift space formed thereby until reaching the region of the gap formed between electrodes 12 and 13. In crossing this second gap the electrons are accelerated to high velocity, electrode 13 being positive with respect to electrode 12 and positive with respect to the electron source or cathode.

Again after passing the gap the electrons are in a drift space which, in comparison to the low velocity drift space within electrode 12, may be termed a high velocity drift space.

I have found that in such a device where'the electron stream is subjected to changes in direct current voltage the effect of space charge depression on the electron velocities becomes aggravated. This is particularly true when the electrons are decelerated as well as when the electron beam current, I is increased. Referring to Figure 3, wherein direct current electron velocity V in the axial or z direction is plotted as a function of location across a beam of diameter 2a and where the point r=0 indicates the center of the beam, it is seen that dotted curve B indicates the axial velocity distribution when space charge is uncorrected while solid curve A indicates the axial beam velocity to be substantially constant across the beam in the instance when space charge is fully magnetically corrected.

The elfect of space charge on the axial electron velocity across the beam as indicated in Figure 3 by curve B and the consequent loss in efficiency in such devices may readily be understood by reference to Figure 2. As will be more fully pointed out, the curves shown in Figure 2 represent ideal operation in a device corrected in accordance with my invention such as that shown in Figure 1. In Figure 2, the points along the axis of the device or in z direction where alternating beam current, i equals zero and alternating beam velocity, v is a maximum represent sharply defined points. However, in a device having an axial electron direct current velocity distribution across the beam such as that of curve B of Figure 3 it is apparent that the electrons in any given cross section of the beam are out of step with the result that there is a blurring or smearing effect. There is then no complete de-bunching, that is to say there are no certain positions along the beam where alternating beam current approaches zero. It will be understood by those skilled in the art that even though space charge is magnetically corrected in accordance with my invention the alternating current can never be reduced to exactly zero in a practical tube structure, and that the best that can be expected is a minimum alternating current that is substantially zero. As in the amplifier described in said Tien and Field article, amplification is obtained when the decelerating gaps, such as that between electrodes 13 and 14 in Figure 1, are located along the beam where the alternating beam velocity v is maximum. The gaps effective to change the amplitude of the alternating beam velocity, such as that between electrodes 13 and 14, must be located along the beam where i =0 in order to attain maximum efficiency whether such a device is utilized for amplification or deamplification.

-It may be well to point out at this time that the wave length of the alternating velocity and current variations in the electron beam herein referred to and shown in Figure 2 is relatively independent of the frequency or frequencies at which the beam is alternating velocity modulated. The wave length of the velocity and current variations in the electron beam, commonly designated plasma wave length or frequency, undergoes little or substantially no change with change in signal frequency over a broad band of signal frequencies. The interdependence of signal frequency and plasma wave length varies with the thickness of the beam with complete independence occurring with a beam of infinite thickness. The computation of plasma wave length correction as well as the theoretical plasma wave length for given electron beams and signal frequency may be readily computed by referring to known publications and is not repeated here; One such publication is an article by W. C. Hahn entitled Small signal theory of velocity modulated electron beams, in vol. 42, June 1939, the General Electric Review, pages 258270. The space charge waves or plasma oscillations of the type here being dealt with are believed to occur effectively only when the ratio of signal voltage to electron beam direct current voltage is small and the axial component of the space charge has a first order effect. This is distinguished from large signal velocity modulation where the effect of the axial component of the space charge may be negligible.

-'In practice, the points where i or v is minimum are readily located by probing along the path of a beam with a high Q minimum-loss resonant cavity tuned to the desired frequency. From Figure 2 it is apparent that the points where v is minimum occur at one quarter and at odd multiples of a quarter wave length from the point Where 'the beam is velocity modulated. This method determines the location of the point or points where i is minimum for the frequency which most conveniently is the center frequency of the frequency band over which the device is to operate.

As will now be more fully described, the device shown in Figure 1 constructed in accordance with my invention has in operation certain positions along the electron stream where alternating electron current equals substantially zero and the gaps are so located that optimum efficiency is attained; the length of the high and low velocity regions each being approximately one quarter or an odd multiple of a quarter of the effective plasma wave length. All electrons in a high-current density electron beam [travel at the same axial speed only where the tangential velocity of each electron is proportional to its distance from the axis of the beam, which condition is known in this art as Brillouin flow. This condition requires for two regions of different beam velocities, V and V with I =l.45 10 B V (beam radius a constant) that 3 2 V2 112 (a) =6 from which g l ;f) (I and a constant) (1) where I 1 =beam current in amperes, B=magnetic flux density in gausses, V=beam velocity in volts,

B =magnetic fiux density in the region where beam velocity is V and B magnetic flux density in the region where beam velocity is V Solving Equation 1 for various values of V /V gives the following tabulation:

It is apparent that as the ratio V /V decreases the ratio of B /B must increase as indicated to maintain Brillouin flow, where the electrons in the beam are rotating about the center of the beam and, in any given cross section of the beam, have the same angular and axial velocity. Considering the general case..-of two regions of different beam velocities where V is greater than V since beam current I is constant, the space charge force on a given electron other than one on the axis of the beam will vary from one region to the other. In the region having beam velocity V the effect of the radially outward component of the space charge force will be greater than in the region of beam velocity V In view of the fourth root relationship between the ratio of the beam velocities and the ratio of the magnetic held of the two regions and as brought out by the above table, the ratio B /B differs from unity "by a relatively small amount. However, when V V is not close to unity then if B though the space charge effect may be corrected in one of the two regions it will not be corrected in the other. Furthermore, when the magnetic field is such that the space charge effect is corrected in the high velocity region, the adverse eiiect of space charge in the low velocity region is aggravated.

In operation, solenoids 17, 81 each establish a magnetic field having a given flux density B while solenoids 80, 82 each establish a magnetic field having another flux density B which is smaller than B The conditions to satisfy Equation 1 may in this manner readily be provided. Alternate electrodes 12, 14 each have a direct current voltage such that beam velocity in the region bounded by them is V while electrodes 13, 15 each have a direct current voltage such that beam velocity is V The disc shaped shields serve as magnetic circuit elements and direct and partition the magnetic flux and shield adjacent regions one from the other. The ratios and are thus readily established in accordance with Equation 1.

Another form of amplifier device is shown in Figure 4 and comprises solenoid 22 which surrounds the portion of envelope 23 shown, functioning in the usual way when energized to set up a homogeneous axial magnetic field. Shields 18' and 20', of magnetic material, are each mounted so as to extend into the gap between adjacent electrodes while shields 19, 21 and 22, of magnetic material, are arranged and function as in Figure 1. While various shapes may be utilized, shields 1 8', 20 are each substantially cup-shaped members having apertures noid 22 provide the necessary magnetic field flux density in accordance with Equation 1 as will now be more fully described. Each pair of shields 2'1, 18' and 18, 119 affect the field set up by solenoid 22 with the result that the magnetic field between each pair of shields along the axis of the electron stream is proportional to the axial length of solenoid 22 which is shunted. Again, the conditions comparable to those necessary to satisfy Equation 1 may readily be provided. As before, electrodes 12, 14 each have a direct current voltage such that beam velocity in the region bounded by them is V while electrodes 13, 15 each have a direct current voltage such that beam velocity is V As pointed out the axial magnetic field intensity B in the region of electrodes 12 and 14 is proportional to the axial length of solenoid 22 between shields 21, 18 and 19, 20 respectively. Similarly, the axial magnetic field intensity B in the region of electrodes 13 and 15 is proportional to the axial length of solenoid 22 between shields 18, 19 and 20', 22 respectively. Thus, B is seen to be less than B and the ratios and are readily established in accordance with Equation 1.

Another form of amplifier device is shown in Figure 5 and comprises solenoid 22 which surrounds the portion of envelope 23 shown. Solenoid 22 and envelope 23 are similar to solenoid 22 and envelope 2 3 in Figure 4. Here, electrodes 24, 25, 26, 27 and 28 are of magnetic material and serve both to establish the alternating low velocity and high velocity drift spaces and the necessary variation in the axial magnetic field in accordance with Equation 1. Electrodes 24, 25, 26, 27 and 28 each has a centrally located aperture, which apertures are axially alined to permit the passage therethrough of an axial electron beam from a source (not shown).

Figure 6 shows a space beam space charge wave amplifier tube 29 constructed in accordance with my invention. An elongated vacuum tight envelope 30 has a convergent gun structure including cathode 31 and focusing electrodes 32, 33 and 34. Between input and output resonant cavities 35, 36 I provide an amplifier section 37 which includes electrodes and shields arranged as shown and somewhat similar to the section shown in Figure 4. Here apertured members 38, 39 form a gap associated with input cavity 35 and serve to velocity modulate the electron beam projected from the gun structure. Electrodes 40 and electrodes 41 are of non-magnetic material, mounted alternately and are utilized to establish low and high velocity drift spaces, respectively. Shields 42, 43 are of magnetic material and with solenoid 44 provide an axial magnetic field of desired intensity for each of the drift spaces formed by electrodes 40 and 41. While the modulator provided here functions substantially as shown in Figure 2, the structure is readily adapted for utilizing a greater number of changes in velocity. Here electrodes 40, 41 as well as shields 42, 43 have outwardly extending annular portions sealed through envelope 30. The portions of electrodes 40, 41 external of envelope 30 provide convenient leads. The external portions of shields 42, 43 extend toward solenoid 44 though are not necessarily in contact therewith.

In operation, amplifier 29 may be operated by a direct current voltage source S as indicated in Figure 6 with cathode 31 at 600 volts, electrodes 40 at -400 volts, electrodes 41 at +400 volts and shields 42, 43 at ground or zero potential. The electron beam is velocity modulated by the input cavity which is coupled to a radio frequency source. When shields 42, 43 extend close to the beam path it is necessary to apply a direct current voltage thereto which is the average of the direct current voltages applied to the adjacent electrodes. Amplifier section 37 I also provide an improved arrangement for deamplitying or reducing substantially to zero undesired signals. For example, such an arrangement is highly useful in a low noise traveling wave tube 55, as shown in Figure 7. Tube 55 may have the usual structure forming an interaction region including an elongated wave guiding means such as helix 56, input and output wave guides 57, 58, focusing magnet or solenoid 59 and collector 60. A shielded convergent flow electron gun structure may conveniently be mounted at one end of envelope 61 and spaced from the interaction region. As is well known, an electron beam projected from known cathodes has a random electron velocity distribution at the cathode which results in a random velocity modulation of the electrons in the beam. This random modulation is superimposed upon the signal velocity modulation of the 'beam which takes place in the interaction region, of the tube through interaction between the electron beam and the high frequency electric field associated with the signal input high frequency waves to be amplified. Thus, the random modulation resulting from the random velocity distribution at the cathode represents noise in the output of the tube.

By inverting the amplifier sections of Figures 1, 4, 5 and 6, I provide, in accordance with my invention, an arrangement for eliminating noise 'by deamplifying or reducing the amplitude of the velocity variations to a minimum. Intermediate the gun structure and the interaction region in Figure 7 I provide an array of apertured electrodes 62, 63 arranged alternately in that sequence. Electrodes 62 function like electrodes 13 of Figure 1 and when energized are adapted to form high velocity drift spaces. Electrodes 63 function like electrodes 12 of Figure -1 and when energized form low velocity drift spaces. Shields 64, 65, 66, 67 and 68 are of magnetic material and function in conjunction with solenoid 69 which surrounds that portion of envelope 61 in which the modulator section is mounted. As shown in Figure 8 the intensity of the axial magnetic field H is changed abruptly to match a change in the direct current voltage V along the modulator section so as to maintain substantially the condition of Equation 1. The broken line indicated by v shows the effect of the direct current voltage discontinuities on the alternating velocity associated with the noise in the electron beam. Each of accelerating gaps at the entrances to electrodes 62 in Figure 7 is located along the beam path substantially at an alternating current (noise) velocity maximum in the beam to obtain noise reduction, as distinguished from the gap location in the amplifier of Fig. 1, for example, as shown by the broken line v in Figure 8. It should be noted that the noise variations or plasma oscillations which are deamplified have a band width of which the center frequency is the same frequency at the center of the frequency band of tube 55. Reference may be had of Figure-6 with the addition of a section for deamplifying noise as shown in the device illustrated in Figure 7. The various parts corresponding to those shown in Figures 6 and 7 are indicated by the same numerals. Device is a low noise space charge wave amplifier comprising a first section following the cathode functioning to eliminate noise, as in Fig. 7, and a second section following the high frequency input functioning as in the device of Figure 6 to provide an amplified signal in the output.

While I have in each instance shown several pairs of high and low voltage electrodes for effecting plural direct current voltage discontinuities, I may use more or less as desired and even as few as only one pair. However, whatever the number of electrodes or voltage discontinuities, that is to say voltage jumps, utilized I provide a magnetic field intensity such that conditions comparable to those of Equation 1 are substantially fulfilled.

It is apparent from the foregoing that to accomplish eflicient amplification or deamplification when subjecting the electron stream to direct current voltage jumps, I maintain the stream substantially in Brillouin flow condition. While I have shown various ways of carrying out my invention, I do not desire my invention to be limited specifically thereto since obvious changes may be effected therein by one familiar with such devices. It may be well to point out at this time that since the relationship of the direct current voltages and magnetic field intensities must be in accordance with Equation 1, things are correlated to attain that end. While adherence to the conditions of Equation 1 is desirable, some tolerance is obviously necessary and unavoidable when such devices are constructed. While close figures on permissible tolerance are not available, it appears at the present time that deviation from the relationship of Equation 1 should not be greater than 10% but possibly a greater departure may be permissible.

What I claim is:

1. An electron device, comprising means for producing an electron beam along a given path and having velocity variations; means coupled to said beam path for changing the amplitude of said variations and comprising at least two hollow electrodes surrounding and spaced along said beam path and adapted when energized to establish therein at least two successive regions of two diiferent direct current voltages, and means coupled to said path for establishing a magnetic field having flux lines substantially parallel to said path with two different magnetic field intensities in said successive regions of two different voltages.

2. An electron device as in claim 1, wherein said magnetic field means establish magnetic field intensities in said successive regions that are higher in the lower voltage regions than in the higher voltage regions.

3. An electron device as in claim 2, wherein said hollow electrodes and corresponding successive regions have substantially different lengths.

4. Electronic apparatus comprising the combination of the electron device described in claim 1 with direct current voltage supply means connected to said electrodes for applying said two different voltages thereto.

5. An electron device as described in claim 1, wherein said means for producing said beam of electrons having velocity variations comprises a cathode adapted to produce a beam having a random electron velocity distribution.

6. An electron device as described in claim 1, wherein said means for producing said beam of electrons having velocity variations comprises an electron gun and means coupled to said beam path beyond said gun for modulating said beam in accordance with a signal.

7. A beam tube, comprising means for producing an electron beam along a given path and having velocity and current variations of a given beam plasma wave length, means coupled to the beam path for changing the amplitude of said variations comprising electrode means 9 for establishing successive regions of high and low direct current voltages along said path, the boundaries between said successive regions being oriented with and substantially coincident with a quarter or an odd multiple of a quarter of said plasma wave length along said beam, and means for establishing along said path an axial magnetic field having a greater intensity in said low voltage region than in said high voltage region.

8. An electron discharge device, comprising means for projecting a beam of electrons along a given path, means for taking an output from said beam along said path, means for velocity modulating the electrons of said beam in accordance with a signal to be amplified, and means coupled to the beam path intermediate said modulating means and said output means for amplifying the amplitude of said velocity variations comprising electrode means for establishing along said path successive regions of high and low direct current voltages N/4 plasma wave lengths of said beam where N is any odd integer and means for establishing along said path an axial magnetic field having a greater intensity in said low voltage region than in said high voltage region.

9. An electron discharge device for operation over a given range of frequencies, comprising means for projecting a beam of electrons along a given path, means coupled to the beam path for velocity modulating the electrons of said beam in accordance with a signal to be amplified, means coupled to the beam path intermediate said electron projecting means and said modulating means for deamplifying the amplitude of a broad band of velocity variations in said beam of which the center frequency corresponds to the given frequency, said deamplifying means comprising electrode means for establishing along said path successive regions of high and low direct current voltages of N /4 plasma wave lengths in said beam where N is any odd integer and means for establishing along said path an axial magnetic field having a greater intensity in said low voltage region than in said high voltage region.

10. An electron discharge device for operation over a given range of frequencies, comprising means for projecting a beam of electrons along a given path, means coupled to the beam path for velocity modulating the electrons of said beam in accordance with a signal to be amplified, means coupled to the beam path intermediate said electron projecting means and said modulating means for deamplifying the amplitude of a broad band of velocity variations in said beam of which the center frequency corresponds to the given frequency, said deamplifying means comprising electrode means for establishing along said path successive regions of high and low direct current voltages of N/ 4 plasma Wave lengths in said beam where N is any odd integer and means for establishing along said path an axial magnetic field having a greater intensity in said low voltage region than in said high voltage region, means for taking an output from said beam and means coupled to said beam path intermediate said modulating means and said output means for amplifying the velocity variations produced by said velocity modulating means and comprising electrode means for establishing along said path successive regions of low and high direct current voltages of N/4 plasma wave lengths of said beam where N is any odd integer and means for establishing along said path an axial magnetic field having a greater intensity in said low voltage region than in said high voltage region.

11. An electron device, comprising means for producing a beam of electrons along a given path having velocity variations, means coupled to the beam path for changing the amplitude of said variations comprising at least two spaced apart electrodes coupled to said beam path, said electrodes being adapted when energized to establish successive regions of two different direct current voltages along said beam path, and means for establishing a mag 10 netic field with magnetic flux lines parallel to the path and including a plurality of magnetic circuit members along said beam path for establishing a region of different magnetic field intensity in each of said regions of different voltage.

12. An electron device, comprising means for producing a beam of electrons along a given path having velocity variations, means coupled to the beam path for changing the amplitude of said variations comprising a plurality of magnetic circuit members spaced apart along the axis of said beam path, said magnetic members defining alternate regions having a given axial extent adjacent said beam path and a second axial extent at a portion more removed from said beam path greater than said given axial extent, the remaining regions having an axial extent adjacent said beam path larger than said given extent and an axial extent at a position more removed from said beam path smaller than said second axial extent, and a plurality of spaced apart electrodes one in each of said regions, the electrodes in said alternate regions being adapted when energized to establish a given direct current voltage and the electrodes in said remaining regions being adapted when energized to establish a direct current voltage higher than said given voltage.

13. An electron device comprising means for producing a beam of electrons along a given path, output means along said path, modulating means coupled to said beam path intermediate said means for producing said electron beam and said output means and for velocity modulating said beam in accordance with a signal to be amplified, amplifying means intermediate said modulating means and said output means and coupled to said beam path for amplifying the amplitude of the velocity variations of the electrons in said beam, said amplifying means comprising at least two spaced apart electrodes along said beam path and adapted when energized to establish successive regions of lower and higher direct current voltage in that sequence intermediate said modulating means and said output means with the region next adjacent said modulating means being a lower voltage region, and means for establishing an axial magnetic field along said path including a plurality of magnetic shielding members one extending in each of the spaces intermediate said modulating means and said electrodes and said output means, said magnetic shielding members being adapted "to establish a region of different magnetic field intensity for each of said diiferent voltage regions and substantially coincident therewith, the higher magnetic field intensity region being in the lower voltage region.

14. An electron device comprising means for producing a beam of electrons along a given path, modulating :means coupled to said beam path and spaced from said means for producing the beam and for modulating said beam in accordance with a signal to be amplified, deamplifying means coupled to said beam path intermediate said means for producing the beam and said modulating means and for decreasing the amplitude of velocity variations of electrons in said beam, said deamplifying means comprising at least two spaced apart electrodes along said beam path and adapted when energized to establish successive regions of higher and lower direct current voltage 'in that sequence intermediate said means for producing the beam and said modulating means with the region 'next adjacent said means for producing the beam being a higher voltage region, and means for establishing a :magnetic field with magnetic flux lines parallel to the path and including a plurality of magnetic shielding members at least one before and after each of said electrodes .in the direction of travel of said beam along said path, said magnetic shielding members being adapted to establish lower and higher magnetic field intensities in said higher and lower voltage regions respectively.

15. An electron discharge device, comprising elongated wave guiding means capable of propagating a traveling Wave therealong, means for projecting an electron beam along said wave guiding means and in energy coupling relation thereto, and means coupled to the beam path intermediate said wave guiding means and said electron beam projecting means for deamplifying the amplitude of a broad band of velocity variations in said beam of which the center frequency corresponds to said wave, said deamplifying means comprising electrode means for establishing along said path successive regions of high and low direct current voltages of N/4 plasma wave lengths in said beam where N is any odd integer and means for establishing along said path an axial magnetic field having a greater intensity in said low voltage region than in said high voltage region.

16. Electronic apparatus comprising means including a cathode for producing along a given path an electron beam having velocity variations, means coupled to the beam path for changing the amplitude of said variations comprising electrode means for establishing successive regions of two different direct-current voltages along said path, direct-current voltage supply means connected to said electrode means for applying said two diiierent voltages thereto, and means for establishing along said path an axial magnetic field having two different intensities/one in each of said regions of different voltages the ratio of said two magnetic field intensities being substantially equal to the fourth root of the inverse ratio of said two voltages, whereby the electrons in any given transverse cross-section of said beam in said regions have substantially the same angular velocity about the axis of said beam and substantially the same velocity along said axis. 9

References Cited in the file of this patent UNITED STATES PATENTS Re. 22,389 Litton Nov. 2, 1942 2,190,511 Cage Feb. 13, 1940 2,222,902 Hahn Nov. 26, 1940 2,247,338 Ramo June 24, 1941 2,347,797 Posthumus et al. May 2, 1944 2,424,965 Brillouin .Aug. 5, 1947 2,538,669 Coeterier Jan. 16, 1951 2,608,668 Hines a- Aug. 26, 1952 

